Demographic evidence that development is not compatible with sustainability in semi-urban freshwater turtles

Habitat loss and fragmentation are primary drivers of biodiversity declines worldwide. Balancing urban development with environmental sustainability is a major challenge that is increasingly recognized in planning decisions. Urban development proposals are often approved with the expectation that deleterious impacts on native species will be constrained and/or mitigated, but this assumption is rarely tested over a sufficient timeline to confirm its validity for long-lived, at-risk species. We tracked changes in Blanding’s turtle (Emydoidea blandingii) habitat availability and demography over 10 years (2010-2020) near Ottawa, ON, Canada, to determine whether approved development and associated mitigation measures were sufficient to ensure long-term population persistence. Suitable turtle habitat declined by ~10% during the decade and wetland corridors were essentially lost. This habitat loss coincided with a marked reduction in adult turtle survival and juvenile recruitment, resulting in a 70% decline in population size. Adult females experienced the greatest decline, and despite wildlife fencing and culvert placement as conditions of project approval, turtle mortality due to vehicle collisions likely was the primary cause of the decline. Population viability analysis revealed that ~4 adult female road mortalities per year reproduced a comparable decline to that observed in our annual population estimates; at this rate the population will likely breach its quasi-extinction threshold in less than a decade. Accordingly, we infer that in our study area approved development was not compatible with at-risk turtle population viability. More broadly, our findings imply that development approval conditions, even when conducted in the context of species-at-risk protection, can be inadequate to ensure sustainability. Thus, we contend that if environmental sustainability is to be prioritized, development projects should be subject to more stringent review and oversight during the planning, approval, and implementation phases.